Lubricant composition

ABSTRACT

A lubricant composition comprising lubricant base oil; (A) from 300 to 3000 ppm by weight, in terms of elemental molybdenum, of a sulphur-containing organomolybdenum complex, based on the total weight of the lubricant composition, wherein the weight ratio of sulphur to molybdenum is in the range of from 1 to 1.4; (B) a zinc dithiocarbamate wherein the amount of sulphur derived from this component relative to the amount of molybdenum derived from component (A) in terms of the weight ratio is in the range of from 0.2 to 4; and (C) one or more calcium salts of organic acids, wherein the amount of calcium derived from this component relative to the amount of molybdenum derived from component (A) in terms of the weight ratio is in the range of from 0.2 to 7.

RELATED CASES

The present application claims priority from Japanese application 2006-041271, filed Feb. 17, 2006, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a lubricant composition, and in particular to a high-performance lubricant composition capable of exhibiting excellent friction reducing characteristics.

BACKGROUND OF THE INVENTION

Lubricants are used in parts subject to sliding friction in various machines such as automotive vehicles, construction machines and machine tools. However, because of the trends towards more compact machinery and higher performance, lubricants having better friction properties are in demand. There is particular demand for lubricants having low friction resistance from the standpoint of reducing energy losses due to friction.

Organomolybdenum compounds such as molybdenum dithiocarbamates or molybdenum dithiophosphates have been widely used in the lubricant compositions of recent years in order to reduce friction, especially at lubrication points in the boundary lubrication regime, since they exhibit an excellent friction-reducing effect.

However, since molybdenum has been designated as a “Class 1” specified chemical substance in accordance with the pollution release and transfer register (PRTR) reporting system set up in 1999 in Japan, it is desirable from the standpoint of environmental protection that the amount of molybdenum used should be as small as possible.

Furthermore, since the price of molybdenum is relatively high and has been rising sharply in recent years, the development of high-performance lubricants in which the amount of molybdenum in the blend has been reduced is also required with a view to improving the economic efficiency of the lubricants.

Organomolybdenum compounds are said to reduce friction by forming a film comprising mainly molybdenum disulphide on the lubrication surfaces by virtue of a frictional reaction. Therefore, if a compound containing sulphur is used at the same time, formation of the molybdenum disulphide film will be promoted and the friction-reducing effect thereof can be enhanced.

Japanese (Laid-Open) Patent Application No. 62-207397 A discloses an example of such a lubricant composition, comprising a combination of sulphurised molybdenum dialkyl dithiocarbamates and a sulphur-phosphor type extreme-pressure additive.

The type of sulphur-containing compounds to be used and the balance of the amounts of additives to be blended in a lubricant composition are also important factors. In order to allow the organomolybdenum compound to be used effectively, the most suitable compounds must be blended in the most suitable proportions.

Thus, it is highly desirable to develop lubricant compositions which are capable of substantially reducing friction at lubrication points by using a smaller molybdenum content than used hitherto, and which compositions also place a lower burden on the environment.

SUMMARY OF THE INVENTION

In the present invention, a lubricant composition has surprisingly been developed which is capable of reducing friction at lubrication points and, by reducing at the same time the amount of molybdenum contained therein, of reducing the burden on the environment.

Accordingly, the present invention provides a lubricant composition comprising lubricant base oil; (A) in the range of from 300 to 3000 ppm by weight, in terms of elemental molybdenum, of a sulphur-containing organomolybdenum complex, based on the total weight of the lubricant composition, wherein the weight ratio of sulphur to molybdenum is in the range of from 1 to 1.4; (B) a zinc dithiocarbamate, wherein the amount of sulphur derived from this component relative to the amount of molybdenum derived from component (A) in terms of the weight ratio is in the range of from 0.2 to 4; and (C) one or more calcium salts of organic acids selected from the group consisting of alkyl phenols, alkyl salicylic acids, aliphatic sulphonic acids and aromatic sulphonic acids, wherein the amount of calcium derived from this component relative to the amount of molybdenum derived from component (A) in terms of the weight ratio is in the range of from 0.2 to 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The lubricant base oils in the lubricant composition of the present invention may be selected from mineral oils, synthetic oils and mixtures thereof. Examples of the mineral-type base oils that may be conveniently used include those refined by one or more treatments such as vacuum distillation of an atmospheric residue obtained by atmospheric distillation of crude oil, or wax-isomerised mineral oils and base oils produced by the process in which GTL wax (gas-to-liquid wax) is isomerised by the Fischer-Tropsch process.

Examples of synthetic oils that may be conveniently used include polyolefins such as α-olefin oligomers and polybutenes, polyalkylene glycols such as polyethylene glycols and polypropylene glycols, diesters such as di-2-ethylhexyl sebacate and di-2-ethylhexyl adipate, polyol esters such as trimethylolpropane esters and pentaerythritol esters, perfluoroalkyl ethers, silicone oils and polyphenyl ethers.

Any one or several of the afore-mentioned oils may be used as the base oil in the present invention, or the base oil may be selected from any known oil composition suitable for functioning as a base oil.

The sulphur-containing organomolybdenum complex used as component (A) in the lubricant composition of the present invention may be conveniently selected from molybdenum dithiocarbamates (MoDTC) and/or molybdenum dithiophosphates (MoDTP).

Preferred molybdenum dithiocarbamates include those according to general formula (I),

wherein R₁ and R₂ are each radicals independently selected from hydrocarbon groups having in the range of from 4 to 18 carbon atoms, m is an integer in the range of from 0 to 3, n is an integer in the range of from 1 to 4 and m+n=4.

Preferred molybdenum dithiophosphates include those according to general formula (II),

wherein R₃ and R₄ are each radicals independently selected from hydrocarbon groups having in the range of from 4 to 18 carbon atoms, m is an integer in the range of from 0 to 3, n is an integer in the range of from 1 to 4 and m+n=4.

While oxygen atoms or sulphur atoms may indiscriminately be linked to the molybdenum atoms that form the core of the afore-mentioned complex that is component (A), said complex preferably has a weight ratio of the amount of sulphur relative to the amount of molybdenum therein in the range of from 1 to 1.4. Said weight ratio may be either for a sulphur-containing organomolybdenum complex alone or for the proportion in the total weight of a mixture of several kinds of sulphur-containing organomolybdenum complexes.

If this weight ratio is less than 1, then the amount of sulphur relative to the molybdenum will be insufficient and an adequate film of molybdenum disulphide will not form on the lubrication surfaces. However, if said weight ratio is greater than 1.4, then the combined effect when blended with the other additives will not be sufficiently obtained and the friction coefficient may rise.

Examples of the afore-mentioned molybdenum dithiocarbamates (MoDTC) include but are not limited to: sulphurised molybdenum dibutyldithiocarbamate, sulphurised molybdenum dipentyldithiocarbamate, sulphurised molybdenum hexyldithiocarbamate, sulphurised molybdenum dioctyldithiocarbamate, sulphurised molybdenum didecyldithiocarbamate, sulphurised molybdenum tridecyldithiocarbamate, sulphurised molybdenum diisobutyldithiocarbamate, sulphurised molybdenum di(2-ethylhexyl)dithiocarbamate, sulphurised molybdenum dilauryldithiocarbamate, sulphurised molybdenum distearyldithiocarbamate, sulphurised molybdenum diphenyldithiocarbamate, sulphurised molybdenum ditolyldithiocarbamate, sulphurised molybdenum dixylyldithiocarbamate, sulphurised molybdenum diethylphenyl dithiocarbamate, sulphurised molybdenum dipropylphenyl dithiocarbamate, sulphurised molybdenum dibutylphenyl dithiocarbamate, sulphurised molybdenum dipentylphenyl dithiocarbamate, sulphurised molybdenum dihexylphenyl dithiocarbamate, sulphurised molybdenum diheptylphenyl dithiocarbamate, sulphurised molybdenum dioctylphenyl dithiocarbamate, sulphurised molybdenum dinonylphenyldithiocarbamate, sulphurised molybdenum didecylphenyldithiocarbamate and sulphurised molybdenum didodecylphenyldithiocarbamate.

Examples of the afore-mentioned molybdenum dithiophosphates (MoDTP) include but are not limited to: sulphurised molybdenum dibutyldithiophosphate, sulphurised molybdenum dipentyldithiophosphate, sulphurised molybdenum dihexyldithiophosphate, sulphurised molybdenum dioctyldithiophosphate, sulphurised molybdenum didecyldithiophosphate, sulphurised molybdenum tridecyldithiophosphate, sulphurised molybdenum diisobutyldithiophosphate, sulphurised molybdenum di(2-ethylhexyl)dithiophosphate, sulphurised molybdenum dilauryldithiophosphate, sulphurised molybdenum distearyldithiophosphate, sulphurised molybdenum diphenyldithiophosphate, sulphurised molybdenum ditolyldithiophosphate, sulphurised molybdenum dixylyldithiophosphate, sulphurised molybdenum diethylphenyl dithiophosphate, sulphurised molybdenum dipropylphenyldithiophosphate, sulphurised molybdenum dibutylphenyl dithiophosphate, sulphurised molybdenum dipentylphenyl dithiophosphate, sulphurised molybdenum dihexylphenyl dithiophosphate, sulphurised molybdenum diheptylphenyl dithiophosphate, sulphurised molybdenum dioctylphenyl dithiophosphate, sulphurised molybdenum dinonylphenyl dithiophosphate, sulphurised molybdenum didecylphenyl dithiophosphate and sulphurised molybdenum didodecylphenyl dithiophosphate.

The amount of the afore-mentioned component (A) in the lubricant composition of the present invention is preferably in the range of from 300 to 3000 ppm by weight, in terms of elemental molybdenum, based on the total weight of the lubricant composition. If the amount of component (A) is less than 300 ppm, in terms of elemental molybdenum, based on the total weight of the lubricant composition, then a sufficient friction-reducing effect is not obtained. Furthermore, if the amount of component (A) is more than 3000 ppm in terms of elemental molybdenum, based on the total weight of the lubricant composition, then the friction may increase and the cost of the lubricant composition will also rise.

The zinc dithiocarbamate (ZnDTC) of the afore-mentioned component (B) may be a compound according to general formula (III),

wherein R₅ and R₆ are each radicals independently selected from hydrocarbon groups having in the range of from 4 to 18 carbon atoms. Preferably, R₅ and R₆ are each independently selected from straight-chain and/or branched groups having in the range of from 4 to 8 carbon atoms.

Examples of zinc dithiocarbamates (ZnDTC) that may be conveniently used include but are not limited to: sulphurised zinc dibutyldithiocarbamate, sulphurised zinc diamyl dithiocarbamate, sulphurised zinc dihexyldithiocarbamate, sulphurised zinc dioctyl dithiocarbamate, sulphurised zinc diisobutyldithiocarbamate and sulphurised zinc di(2-ethylhexyl)dithiocarbamate.

The amount of the afore-mentioned component (B) that is incorporated in the lubricant composition of the present invention is such that the amount of sulphur derived from component (B) relative to the amount of molybdenum derived from the afore-mentioned component (A) in terms of the weight ratio is in the range of from 0.2 to 4. If said weight ratio is less than 0.2, then a film of molybdenum disulphide effective enough to reduce friction on the lubrication surfaces may not form. Furthermore, if said weight ratio is greater than 4, then the friction-reducing function of the sulphur-containing organomolybdenum complex (A) is hindered and the friction properties may even deteriorate.

The afore-mentioned component (C) is preferably a compound known as a metallic detergent. Hitherto, barium, magnesium and calcium phenates, salicylates and sulphonates have generally been used as metallic detergents. In the present invention, preferably at least one detergent selected from the group comprised of calcium phenates, calcium salicylates and calcium sulphonates is incorporated in the blend.

These metallic detergents are often subjected to an overbasing treatment, generally by incorporating a metallic carbonate during the manufacturing process. The extent of the overbasing is shown by the total base number (TBN). The TBN of a normally manufactured detergent is typically within the range of from 0 to 500 mgKOH/g. There is no particular restriction on the TBN of the calcium salts of organic acids used in the lubricant composition of the present invention and a broad range can be used from neutral to overbased.

The amount of the afore-mentioned component (C) incorporated in the lubricant composition of the present invention is preferably such that the amount of calcium derived from this component (C) relative to the amount of molybdenum derived from the afore-mentioned component (A) in terms of the weight ratio is in the range of from 0.2 to 7. If said weight ratio is less than 0.2, then sufficient friction-reducing effect may not be obtained, and if said weight ratio is greater than 7, then the friction-reducing function is hindered and the friction properties may even deteriorate.

The lubricant composition of the present invention may optionally further comprise (D) one or more simple metallic soaps, complex metallic soaps thereof and/or urea compounds, i.e. to form a grease.

Such simple and complex metallic soaps may be metallic salts of fatty acids or mixtures of fatty acids. Preferred fatty acids in the present invention are stearic acid and 12-hydroxystearic acid. Preferred simple and complex metallic soaps are lithium soaps, calcium soaps, sodium soaps and aluminium soaps.

These metallic soaps (D) may be obtained by reacting acids or acid mixtures in particular fatty acids or fatty acid mixtures with a metal hydroxide. Said soaps may be reacted in advance and added to the lubricant base oil or they may be reacted within the lubricant base oil.

Accordingly, in a preferred embodiment, the lubricant composition of the present invention may optionally comprise (D) one or more compounds selected from the group consisting of lithium soaps, calcium soaps, sodium soaps, aluminium soaps, complex soaps thereof and urea compounds.

The afore-mentioned urea compounds may be conveniently selected from diurea, triurea and/or tetraurea compounds. In the present invention, diurea compounds as illustrated by general formula (IV)

wherein the hydrocarbon groups located at the terminal positions of the chemical structural formula, R₈ and R₉, may be the same or different and each have in the range of from 8 to 18 carbon atoms and where the hydrocarbon group R₇ located in the centre of the chemical structural formula is a hydrocarbon group containing an aromatic ring having in the range of from 6 to 15 carbon atoms.

The afore-mentioned urea compounds may be obtained by reacting diisocyanates and monoamines. Examples of such diisocyanates include diphenylmethane diisocyanate, phenylene diisocyanate, diphenyl diisocyanate, phenyl diisocyanate and tolylene diisocyanate. Examples of such monoamines include octylamine, dodecylamine, hexadecylamine and octadecylamine.

Such diisocyanates and monoamine compounds may either be reacted in advance and the resulting urea compounds added to the lubricant base oil or said diisocyanates and monoamines may be reacted in situ within the lubricant base oil. Also, the afore-mentioned metallic soaps and urea compounds may be used mixed together.

It is preferred that when said one or more components (D) are present in the lubricant composition, they are present in a total amount in the range of from 2 to 30% by weight, more preferably in an amount in the range of from 5 to 20% by weight, based on the total weight of the lubricant composition. In this way, the lubricant may be made more viscous. If the level of said component (D) exceeds 30% by weight, based on the total weight of the lubricant composition, then the lubricant composition may be too viscous, and there will be a risk that sufficient lubricant will not spread across the friction surfaces.

Thus, in a preferred embodiment, the lubricant composition of the present invention further comprises component (D) in the range of from 2 to 30% by weight of one or more compounds selected from the group consisting of lithium soaps, calcium soaps, sodium soaps, aluminium soaps, complex soaps thereof and urea compounds, based on the total weight of the lubricant composition.

In order to improve performance further, it is possible to incorporate in the lubricant composition of the present invention, according to purpose and application, suitable amounts of anti-oxidants, corrosion inhibitors, extreme-pressure agents, polymers, metal deactivators and any other additives.

The present invention further provides a method of reducing friction in the bearings, gears and/or joints of mechanical devices, wherein said method comprises lubricating said bearings, gears and/or joints with a lubricant composition as hereinbefore described.

In addition, the present invention also provides a bearing, gear and joint, characterised in that the lubricant composition as hereinbefore described is used therein as the lubricant.

Furthermore, the present invention also provides the use of a lubricant composition as hereinbefore described to lubricate a bearing, a gear and/or a joint of a mechanical device, and in particular to reduce friction therein.

Certain embodiments of the present invention are described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES Examples 1, 2, 5-8; Comparative Examples 1, 3, 6, 8

Following the blend amounts shown in Tables 1, 2, 4 and 5, diphenylmethane-4-4′-diisocyanate (MDI) containing an aromatic ring was added to a portion of mineral oil (kinematic viscosity at 40° C.: 100 mm²/s) used as the lubricant base oil, and these mixtures were heated. A monoamine was added to another portion of the same mineral oil and dissolved by heating. The two afore-mentioned solutions in lubricant base oils were mixed together and reacted. After cooling, the various components (A), (B) and (C) were added so as to give the proportions shown in the Tables. After a homogenising treatment using a three roll mill, the lubricant compositions of Examples 1, 2 and 5-8 and Comparative Examples 1, 3, 6 and 8 were prepared.

Examples 9, 10; Comparative Examples 2, 4, 5, 7

Following the blend amounts shown in Tables 2, 4 and 5 and using a mineral oil (kinematic viscosity at 40° C.: 100 mm²/s) as the lubricant base oil, lithium stearate or lithium 12-hydroxystearate was dissolved therein by heating. After cooling, the various components (A), (B) and (C) were added so as to give the proportions shown in the Tables. After a homogenising treatment using a three roll mill, the lubricant compositions of Examples 9 and 10 and Comparative Examples 2, 4, 5 and 7 were prepared.

Examples 3, 4

Following the blend amounts shown in Table 1, diphenylmethane-4-4′-diisocyanate (MDI) was added to a portion of mineral oil (kinematic viscosity at 40° C.: 100 mm²/s) used as the lubricant base oil, and these mixtures were heated. A monoamine was added to the rest of the mineral oil and dissolved by heating. The two afore-mentioned solutions in lubricant base oils were mixed together and reacted, and lithium stearate or lithium 12-hydroxystearate was dissolved therein by heating. After cooling again, the various components (A), (B) and (C) were added so as to give the proportions shown in Table 1. After a homogenising treatment using a three roll mill, the lubricant compositions of Examples 3 and 4 were prepared.

Examples 11, 12

Following the blend amounts shown in Table 3, and using a mineral oil (kinematic viscosity at 40° C.: 100 mm²/s) as the lubricant base oil, the various components (A), (B) and (C) were added so as to give the proportions shown in Table 3, and the lubricant compositions of Examples 11 and 12 were prepared.

In the afore-mentioned Tables 1-5:

the “MoDTC” of component (A) was a sulphurised molybdenum dialkyldithiocarbamate, the alkyl group having 13 carbon atoms (but the MoDTC used in Comparative Example 1 had 4 carbon atoms);

the “MoDTP” of component (A) was a sulphurised molybdenum dialkyldithiophosphate, the alkyl group having 8 carbon atoms;

the “ZnDTC” of component (B) was a zinc dialkyldithiocarbamate, the alkyl group having 5 carbon atoms; and

the “diurea” of component (D) was the reaction product of MDI and a monoamine, the monoamine being octylamine and/or oleylamine.

Property Evaluation Experiments

The properties in respect of the lubricant compositions of the various examples and comparative examples were evaluated by means of the experimental methods below.

-   (1) Penetration

Measured in accordance with the penetration test method of JIS K2220.

-   (2) Dropping point

Measured in accordance with the dropping point test method of JIS K2220.

-   (3) Friction coefficient

Oscillating friction and wear tests (SRV tests) were carried out under the following conditions, and the friction coefficient measured. The duration of the test was 15 minutes and the friction coefficient upon completion (after 15 minutes) was obtained.

Test machine: SRV test rig (manufactured by Optimol)

Surface pressure: 2160 MPa

Sliding speed: 0.200 m/s

Temperature: 30° C.

Test ball: diameter 17.5 mm (SUJ2)

Test plate: diameter 24 mm, thickness 7.85 mm (SUJ2)

Results of the Experiments

The results obtained are shown in Tables 1-5. However, in the case of the lubricant compositions of Examples 11 and 12, it was not possible to measure the afore-mentioned penetration (1) and dropping point (2) because there was not enough viscosity.

Evaluation/Discussion

In Examples 1-12, the friction coefficients were extremely low at 0.021-0.030. In the prior art relating to lubricants, achieving a friction coefficient of 0.030 or less has been regarded as extremely difficult. In the art, such friction coefficients have not been obtained unless a substantial amount of organic molybdenum (in the amount of 5000 ppm or more in terms of conversion to elemental molybdenum) has been incorporated in the lubricant composition.

In Comparative Example 1 and Comparative Example 2, the weight ratios of the sulphur in component (A) and the molybdenum (S/Mo ratio) were outside the range of from 1 to 1.4, and in Comparative Example 3 and Comparative Example 6 the converted elemental amounts of molybdenum derived from component (A) were 250 and 4000 and so were outside the range of from 300 to 3000. Also, in Comparative Example 4 and Comparative Example 6 the amounts of sulphur derived from component (B) in terms of the weight ratio to molybdenum were 5.1 and 0.1, and so were outside the range of from 0.2 to 4. In Comparative Example 5, Comparative Example 7 and Comparative Example 8 the amounts of calcium derived from component (C) in terms of the weight ratio to molybdenum were 10.3, 0.1 and 8.7, and so were outside the range of from 0.2 to 7. Furthermore, in Comparative Example 8, the amount of constituent (D) was 35% by weight and so was outside the preferred range of from 2 to 30% by weight. The friction coefficients of the lubricant compositions of these Comparative Examples 1 to 8 ranged from 0.072 to 0.142 and were extremely high compared with the friction coefficients of the afore-mentioned examples according to the present invention, or burning occurred. Therefore, the lubricant composition of the present invention has superior friction characteristics, and can be seen to be an excellent lubricant.

While preferred embodiments of the invention have been described herein, it will be understood that variations may be made without departing from the scope of the invention, as defined in the claims that follow. TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Lubricant base oil (wt %) 84.8  84.0  83.1  82.4  85.3  (A) Amount of Mo derived from MoDTC 850    400    1300    700    1700    (wt ppm) Amount of Mo derived from MoDTP — — — — — (wt ppm) Amount of constituent (A) added in 1.7 0.8 2.7 1.4 3.1 total composition (wt %) S/Mo weight ratio 1.2 1.3 1.2 1.3 1.1 (B) Amount of S derived from ZnDTC 1250    1560    1100    1600    1200    (wt ppm) Amount of constituent (B) added in 1.0 1.2 0.9 1.3 1.1 total composition (wt %) Weight ratio of S to amount of Mo 1.5 3.9 0.8 2.3 0.7 (C) Amount of Ca derived from Ca phenate — — — 985    — (wt ppm) Amount of Ca derived from Ca — — 1125    — 5500    salicylate (wt ppm) Amount of Ca derived from Ca 5220    1300    — — — sulphonate (wt ppm) Amount of constituent (C) added in 4.5 4.0 4.3 4.9 5.5 total composition (wt %) Weight ratio of Ca to amount of Mo 6.1 3.3 0.9 1.4 3.2 (D) Diurea (wt %) 8   10   6   8   5   Lithium stearate (wt %) — — 3   — — Lithium 12-hydroxystearate (wt %) — — — 2   — Results of Worked penetration 296    271    288    274    319    experiments Dropping point (° C.) 212    241    197    203    216    Friction coefficient from SRV test  0.027  0.027  0.025  0.030  0.030

TABLE 2 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Lubricant base oil (wt %) 82.7 81.9 75.8 81.3 75.2 (A) Amount of Mo derived from MoDTC — — 1800 850 700 (wt ppm) Amount of Mo derived from MoDTP 2800 2000 — — — (wt ppm) Amount of constituent (A) added in 3.1 2.2 3.5 1.7 1.5 total composition (wt %) S/Mo weight ratio 1.2 1.1 1.1 1.2 1.3 (B) Amount of S derived from ZnDTC 900 1620 1500 1200 1600 (wt ppm) Amount of constituent (B) added in 0.7 1.3 1.2 1.0 1.3 total composition (wt %) Weight ratio of S to amount of Mo 0.3 0.8 0.8 1.4 2.3 (C) Amount of Ca derived from Ca phenate — — 4160 — — (wt ppm) Amount of Ca derived from Ca — 1125 — 4120 2700 salicylate (wt ppm) Amount of Ca derived from Ca 735 — — — — sulphonate (wt ppm) Amount of constituent (C) added in 3.5 4.6 4.5 4.0 4.0 total composition (wt %) Weight ratio of Ca to amount of Mo 0.2 0.6 2.3 4.9 3.96 (D) Diurea (wt %) 10 10 15 — — Lithium stearate (wt %) — — — — 18 Lithium 12-hydroxystearate (wt %) — — — 12 — Results of Worked penetration 276 283 266 276 264 experiments Dropping point (° C.) 236 224 259 186 190 Friction coefficient from SRV test 0.028 0.030 0.026 0.030 0.029

TABLE 3 Ex. 11 Ex. 12 Lubricant base oil (wt %) 94.1 94.0 (A) Amount of Mo derived from MoDTC (wt ppm) 440 600 Amount of Mo derived from MoDTP (wt ppm) — — Amount of constituent (A) added in total composition (wt %) 0.9 1.2 S/Mo weight ratio 1.2 1.2 (B) Amount of S derived from ZnDTC (wt ppm) 1200 960 Amount of constituent (B) added in total composition (wt %) 1.0 0.8 Weight ratio of S to amount of Mo 2.7 1.6 (C) Amount of Ca derived from Ca phenate (wt ppm) — — Amount of Ca derived from Ca salicylate 2700 — (wt ppm) Amount of Ca derived from Ca sulphonate — 1200 (wt ppm) Amount of constituent (C) added in total composition (wt %) 4.0 4.0 Weight ratio of Ca to amount of Mo 6.1 2.0 (D) Diurea (wt %) — — Lithium stearate (wt %) — — Lithium 12-hydroxystearate (wt %) — — Results of Worked penetration — — experiments Dropping point (° C.) — — Friction coefficient from SRV test 0.021 0.022

TABLE 4 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Lubricant base oil (wt %) 82.2 81.2 87.5 80.8 83.7 (A) Amount of Mo derived from 2000 — 250 430 — MoDTC (wt ppm) Amount of Mo derived from — 2500 — — 500 MoDTP (wt ppm) Amount of constituent (A) 4.8 3.0 0.5 0.9 0.6 added in total composition (wt %) S/Mo weight ratio 0.6 1.5 1.2 1.2 1.1 (B) Amount of S derived from 1200 1620 900 2200 1450 ZnDTC (wt ppm) Amount of constituent (B) added 1.0 1.3 0.8 1.8 1.2 in total composition (wt %) Weight ratio of S to amount of 0.6 0.6 3.6 5.1 2.9 Mo (C) Amount of Ca derived from Ca — — — 950 5150 phenate (wt ppm) Amount of Ca derived from Ca 2700 — — — — salicylate (wt ppm) Amount of Ca derived from Ca — 5200 945 — — sulphonate (wt ppm) Amount of constituent (C) added 4.0 4.5 3.2 4.5 5.5 in total composition (wt %) Weight ratio of Ca to amount of 1.3 2.1 3.8 2.2 10.3 Mo (D) Diurea (wt %) 8 — 8 — — Lithium stearate (wt %) — — — 12 — Lithium 12-hydroxystearate — 10 — — 9 (wt %) Results of Worked penetration 284 272 294 289 273 experiments Dropping point (° C.) 254 191 247 190 185 Friction coefficient from SRV 0.137 0.133 0.142 0.080 Burning test

TABLE 5 Comp. Comp. Comp. Ex. 6 Ex. 7 Ex. 8 Lubricant base oil (wt %) 80.3 81.7 58.1 (A) Amount of Mo derived from MoDTC (wt ppm) 4000 — 600 Amount of Mo derived from MoDTP (wt ppm) — 2800 — Amount of constituent (A) added in total 8.2 3.1 1.4 composition (wt %) S/Mo weight ratio 1.2 1.1 1.2 (B) Amount of S derived from ZnDTC (wt ppm) 600 1560 1250 Amount of constituent (B) added in total 0.5 1.3 1.0 composition (wt %) Weight ratio of S to amount of Mo 0.1 0.4 2.1 (C) Amount of Ca derived from Ca phenate — — — (wt ppm) Amount of Ca derived from Ca salicylate 2700 — — (wt ppm) Amount of Ca derived from Ca sulphonate — 400 5220 (wt ppm) Amount of constituent (C) added in total 4.0 1.9 4.5 composition (wt %) Weight ratio of Ca to amount of Mo 0.7 0.1 8.7 (D) Diurea (wt %) 7 — 35 Lithium stearate (wt %) — 12 — Lithium 12-hydroxystearate (wt %) — — — Results of Worked penetration 302 274 143 experiments Dropping point (° C.) 253 193 262 Friction coefficient from SRV test 0.072 0.083 Burning 

1. A lubricant composition comprising a lubricant base oil and: (A) in the range of from 300 to 3000 ppm by weight, in terms of elemental molybdenum, of a sulphur-containing organomolybdenum complex, based on the total weight of the lubricant composition, wherein the weight ratio of sulphur to molybdenum is in the range of from 1 to 1.4; (B) a zinc dithiocarbamate wherein the amount of sulphur derived from this component relative to the amount of molybdenum derived from component (A) in terms of the weight ratio is in the range of from 0.2 to 4; and (C) one or more calcium salts of organic acids selected from the group consisting of alkyl phenols, alkyl salicylic acids, aliphatic sulphonic acids and aromatic sulphonic acids, wherein the amount of calcium derived from this component relative to the amount of molybdenum derived from component (A) in terms of the weight ratio is in the range of from 0.2 to
 7. 2. The lubricant composition according to claim 1, where said lubricant further comprises a component (D) selected from the group consisting of simple metallic soaps, complex metallic soaps thereof, urea compounds and combinations thereof.
 3. The lubricant composition according to claim 2, wherein said lubricant composition further comprises a compound (D) selected from the group consisting of lithium soaps, calcium soaps, sodium soaps, aluminium soaps, complex soaps thereof, urea compounds and mixtures thereof.
 4. The lubricant composition according to claim 2, wherein component (D) is present in a total amount in the range of from 2 to 30% by weight, based on the total weight of the lubricant composition.
 5. The lubricant composition according to claim 1, wherein the sulphur-containing organomolybdenum complex used as component (A) is selected from the group consisting of molybdenum dithiocarbamates, molybdenum dithiophosphates, and mixtures thereof.
 6. The lubricant composition according to claim 1, wherein the sulphur-containing organomolybdenum complex used as component (A) comprises a molybdenum dithiocarbamate complex having the general formula (I),

wherein R₁ and R₂ are each radicals independently selected from hydrocarbon groups having in the range of from 4 to 18 carbon atoms, m is an integer in the range of from 0 to 3, n is an integer in the range of from 1 to 4 and m+n=4.
 7. The lubricant composition according to claim 1, wherein the sulphur-containing organomolybdenum complex used as component (A) comprises a molybdenum dithiophosphates complex having the general formula (II),

wherein R₃ and R₄ are each radicals independently selected from hydrocarbon groups having in the range of from 4 to 18 carbon atoms, m is an integer in the range of from 0 to 3, n is an integer in the range of from 1 to 4 and m+n=4.
 8. The lubricant composition according to claim 1, wherein the zinc dithiocarbamate used as component (B) comprises a compound having the general formula (III),

wherein R₅ and R₆ are each radicals independently selected from hydrocarbon groups having in the range of from 4 to 18 carbon atoms.
 9. A method of reducing friction in bearings, gears or joints of mechanical devices, wherein said method comprises lubricating said bearings, gears or joints with a lubricant composition according to claim
 1. 10. Use of a lubricant composition according to claim 1 to reduce friction in a bearing, a gear or a joint of a mechanical device. 